Nondestructive testing (NDT) has proven to be an important technique in quality control and safety testing. An NDT system that employs a probe signal is referenced as an xe2x80x9cactive system.xe2x80x9d A well known type of active NDT system uses an ultrasonic probe signal for detecting defects and non-uniformities in structures or layers without destroying or damaging the sample under study. An acoustic transducer generates an ultrasonic probe signal that impinges on a sample under study. A second acoustic transducer receives an acoustic emission signal from the test sample that results from perturbation of the original probe signal due to interfaces, structural changes or defects in the material. Disadvantages of NDT systems that use ultrasonic techniques include complexity in quantitative analysis due to the need to decouple parasitic acoustic signals between the source and the detectors. Acoustic emission (AE) analysis is also used in NDT applications such as: detecting and locating faults in pressure vessels, storage tanks, pipe systems, and also in corrosion processes. Another type of NDT technique employs a xe2x80x9cpassive systemxe2x80x9d which uses an acoustic detector but no acoustic excitation source. A disadvantage of a passive system is that it may only be used to estimate the amount of damage in the material or how long a component will last. Another disadvantage of a passive system is that signals are typically smaller because there is no means to increase the level of the stimuli to increase signals. Furthermore, service environments are very noisy and AE signals tend to be very weak, thus signal discrimination and noise reduction are difficult. Another example of an NDT system uses liquid penetrant as a means of inspection. In a liquid penetrant system, a fluorescent or colored dye contrast liquid penetrant is deposited on a test article. The liquid penetrant is allowed to penetrate into the test article by capillary action into any surface defects. Analysis is achieved by illuminating the test article with ultraviolet or visible light to observe fluorescence or image changes. Then the test article is cleaned by use of a solvent. Shortcomings of using a penetrant include the requirement of a multiple step process, incompatibility between the penetrant and or solvent with the test article, containment of excess penetrant liquid, and limited detection of subsurface defects.
Thus, it may be appreciated that a need exists for a nondestructive technique for detecting defects and non-uniformities in structures or layers without destroying or damaging the sample under study which avoids the inherent limitations and difficulties of the prior art.
A nondestructive acoustic emission testing system using electromagnetic excitation, comprises: a) an electromagnetic wave generator for generating electromagnetic waves that stimulate a test sample to generate acoustic energy; b) an acoustic energy sensor for detecting the acoustic energy and generating a first output signal that represents the acoustic energy; and c) a data processor for comparing the output signal with a reference and for generating a second output signal that represents a characteristic of the test sample.